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LangChain提供了一个回调系统,允许您挂接到LLM应用程序的各个阶段。这对于日志记录、监视、流式传输和其他任务非常有用。
0. LangChain Callbacks模块提供的Callback接口一览
class BaseCallbackHandler:"""Base callback handler that can be used to handle callbacks from langchain."""def on_llm_start(self, serialized: Dict[str, Any], prompts: List[str], **kwargs: Any) -> Any:"""Run when LLM starts running."""def on_chat_model_start(self, serialized: Dict[str, Any], messages: List[List[BaseMessage]], **kwargs: Any) -> Any:"""Run when Chat Model starts running."""def on_llm_new_token(self, token: str, **kwargs: Any) -> Any:"""Run on new LLM token. Only available when streaming is enabled."""def on_llm_end(self, response: LLMResult, **kwargs: Any) -> Any:"""Run when LLM ends running."""def on_llm_error(self, error: Union[Exception, KeyboardInterrupt], **kwargs: Any) -> Any:"""Run when LLM errors."""def on_chain_start(self, serialized: Dict[str, Any], inputs: Dict[str, Any], **kwargs: Any) -> Any:"""Run when chain starts running."""def on_chain_end(self, outputs: Dict[str, Any], **kwargs: Any) -> Any:"""Run when chain ends running."""def on_chain_error(self, error: Union[Exception, KeyboardInterrupt], **kwargs: Any) -> Any:"""Run when chain errors."""def on_tool_start(self, serialized: Dict[str, Any], input_str: str, **kwargs: Any) -> Any:"""Run when tool starts running."""def on_tool_end(self, output: str, **kwargs: Any) -> Any:"""Run when tool ends running."""def on_tool_error(self, error: Union[Exception, KeyboardInterrupt], **kwargs: Any) -> Any:"""Run when tool errors."""def on_text(self, text: str, **kwargs: Any) -> Any:"""Run on arbitrary text."""def on_agent_action(self, action: AgentAction, **kwargs: Any) -> Any:"""Run on agent action."""def on_agent_finish(self, finish: AgentFinish, **kwargs: Any) -> Any:"""Run on agent end."""
1. 最常用的Callback:StdOutCallbackHandler
StdOutCallbackHandler将所有事件的日志作为标准输出,打印到终端中。
注意: 当
verbose
参数设置为true
时,StdOutCallbackHandler
是被默认启用的,也就是你看到的它将运行过程的日志全部打印到了终端窗口中。
上示例:
from langchain.callbacks import StdOutCallbackHandler
from langchain.chains import LLMChain
from langchain_openai import OpenAI
from langchain.prompts import PromptTemplatehandler = StdOutCallbackHandler()
llm = OpenAI()
prompt = PromptTemplate.from_template("1 + {number} = ")# Constructor callback: First, let's explicitly set the StdOutCallbackHandler when initializing our chain
chain = LLMChain(llm=llm, prompt=prompt, callbacks=[handler])
chain.invoke({"number":2})# Use verbose flag: Then, let's use the `verbose` flag to achieve the same result
chain = LLMChain(llm=llm, prompt=prompt, verbose=True)
chain.invoke({"number":2})# Request callbacks: Finally, let's use the request `callbacks` to achieve the same result
chain = LLMChain(llm=llm, prompt=prompt)
chain.invoke({"number":2}, {"callbacks":[handler]})
输出:
对代码和运行结果的解释:
从运行结果可以看出,三次输出的结果相同。再看代码,用三种方式实现了StdOutCallbackHandler
的设置。
- 第一种:
chain = LLMChain(llm=llm, prompt=prompt, callbacks=[handler])
,chain中直接在callbacks中将callback handler传入 - 第二种:使用
verbose=True
,即使不显式声明callbacks,它也使用StdOutCallbackHandler
- 第三种:
chain.invoke({"number":2}, {"callbacks":[handler]})
,在invoke时传入callbacks
2. 各种类型的CallBack实践
2.1 通用 callback:BaseCallbackHandler
实现一个自己的Callback handler,继承自BaseCallbackHandler,然后重写自己需要的回调函数即可。
from langchain.callbacks.base import BaseCallbackHandler
from langchain.schema import HumanMessage
from langchain_openai import ChatOpenAIclass MyCustomHandler(BaseCallbackHandler):def on_llm_new_token(self, token: str, **kwargs) -> None:print(f"My custom handler, token: {token}")# To enable streaming, we pass in `streaming=True` to the ChatModel constructor
# Additionally, we pass in a list with our custom handler
chat = ChatOpenAI(max_tokens=25, streaming=True, callbacks=[MyCustomHandler()])chat([HumanMessage(content="Tell me a joke")])
运行结果:
2.2 异步 CallBack:AsyncCallbackHandler
有时候我们可能在CallBack内做大量的数据处理,可能比较耗时,如果使用通用 CallBack,会阻塞主线程运行,这时候异步 CallBack就比较有用了。
实现一个自己的Callback handler,继承自AsyncCallbackHandler,然后重写自己需要的回调函数即可。
class MyCustomAsyncHandler(AsyncCallbackHandler):"""Async callback handler that can be used to handle callbacks from langchain."""...... 重写相关回调函数 ......
2.3 写日志 / 日志文件: FileCallbackHandler
开发项目过程中,写日志是重要的调试手段之一。正式的项目中,我们不能总是将日志输出到终端中,这样无法传递和保存。
from langchain.callbacks import FileCallbackHandler
from langchain.chains import LLMChain
from langchain.prompts import PromptTemplate
from langchain_openai import OpenAIlogfile = "output.log"handler = FileCallbackHandler(logfile)llm = OpenAI()
prompt = PromptTemplate.from_template("1 + {number} = ")# this chain will both print to stdout (because verbose=True) and write to 'output.log'
# if verbose=False, the FileCallbackHandler will still write to 'output.log'
chain = LLMChain(llm=llm, prompt=prompt, callbacks=[handler], verbose=True)
answer = chain.run(number=2)
运行结果:
题外话:上面的log文件打开后有点乱码,可以用下面方法解析展示出来:
pip install --upgrade ansi2html
pip install ipython
from ansi2html import Ansi2HTMLConverter
from IPython.display import HTML, displaywith open("output.log", "r") as f:content = f.read()conv = Ansi2HTMLConverter()
html = conv.convert(content, full=True)display(HTML(html))
2.4 Token计数:get_openai_callback
Token就是Money,所以知道你的程序运行中使用了多少Token也是非常重要的。通过get_openai_callback
来获取token消耗。
from langchain.callbacks import get_openai_callback
from langchain_openai import OpenAIllm = OpenAI(temperature=0)
with get_openai_callback() as cb:llm("What is the square root of 4?")total_tokens = cb.total_tokens
print("total_tokens: ", total_tokens)## 输出结果:total_tokens: 20
3. 总结
本文我们学习了LangChain的Callbacks模块,实践了各种 CallBack 的用法,知道了怎么利用LangChain进行写日志文件、Token计数等。这对于我们debug程序和监控程序的各个阶段非常重要。
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